Summary
Expression of the immediate-early gene c-fos, a marker of
neuronal activation was employed in adult anesthetized
non-decerebrate cats, in order to localize the brainstem
neuronal populations functionally related to sniff-like
(gasp-like) aspiration reflex (AR). Tissues were immunoprocessed
using an antibody raised against amino acids of Fos and the
avidin-biotin peroxidase complex method. The level of Fos-like
immunoreactivity (FLI) was identified and counted in particular
brainstem sections under light microscopy using PC software
evaluations in control, unstimulated cats and in cats where the
AR was elicited by repeated mechanical stimulation of the
nasopharyngeal region. Fourteen brainstem regions with FLI
labeling, including thirty-seven nuclei were compared for the
number of labeled cells. Compared to the control, a
significantly enhanced FLI was determined bilaterally in animals
with the AR, at various medullary levels. The areas included the
nuclei of the solitary tract (especially the dorsal,
interstitial and ventrolateral subnuclei), the ventromedial part
of the parvocellular tegmental field (FTL - lateral nuclei of
reticular formation), the lateral reticular nucleus, the
ambigual and para-ambigual regions, and the retrofacial nucleus.
FLI was also observed in the gigantocellular tegmental field
(FTG - medial nuclei of reticular formation), the spinal
trigeminal nucleus, in the medullar raphe nuclei (ncl. raphealis
magnus and parvus), and in the medial and lateral vestibular
nuclei. Within the pons, a significant FLI was observed
bilaterally in the parabrachial nucleus (especially in its
lateral subnucleus), the Kölliker-Fuse nucleus, the nucleus
coeruleus, within the medial region of brachium conjunctivum, in
the ventrolateral part of the pontine FTG and the FTL. Within
the mesencephalon a significantly enhanced FLI was found at the
central tegmental field (area ventralis tegmenti Tsai),
bilaterally. Positive FLI found in columns extending from the
caudal medulla oblongata, through the pons up to the
mid-mesencephalon suggests that the aspiration reflex is thus
co-ordinated by a long loop of medullary-pontine-mesencephalic
control circuit rather than by a unique “center“.